Fuel cells have been used as a power source in many applications. For example, fuel cells have been proposed for use in electrical vehicular power plants to replace internal combustion engines. In proton exchange membrane (PEM) type fuel cells, hydrogen is supplied to the anode of the fuel cell and oxygen is supplied as the oxidant to the cathode. PEM fuel cells include a membrane electrode assembly (MEA) comprising a thin, proton transmissive, non-electrically conductive, solid polymer electrolyte membrane having the anode catalyst on one face and the cathode catalyst on the opposite face. The MEA is sandwiched between a pair of non-porous, electrically conductive elements or plates which (1) serve as current collectors for the anode and cathode, and (2) contain appropriate channels and/or openings formed therein for distributing the fuel cell's gaseous reactants over the surfaces of the respective anode and cathode catalysts.
The term “fuel cell” is typically used to refer to either a single cell or a plurality of cells (stack) depending on the context. A plurality of individual cells are typically bundled together to form a fuel cell stack and are commonly arranged in electrical series. Each cell within the stack includes the membrane electrode assembly (MEA) described earlier, and each such MEA provides its increment of voltage. A group of adjacent cells within the stack is referred to as a cluster.
In PEM fuel cells, hydrogen (H2) is the anode reactant (i.e., fuel) and oxygen is the cathode reactant (i.e., oxidant). The oxygen can be either a pure form (O2) or air (a mixture of O2 and N2). The solid polymer electrolytes are typically made from ion exchange resins such as perfluoronated sulfonic acid. The anode/cathode typically comprises finely divided catalytic particles, which are often supported on carbon particles, and mixed with a proton conductive resin. The catalytic particles are typically costly precious metal particles. As such these MEAs are relatively expensive to manufacture and require certain conditions, including proper water management and humidification and control of catalyst fouling constituents such as carbon monoxide (CO), for effective operation.
The electrically conductive plates sandwiching the MEAs may contain an array of grooves in the faces thereof that define flow fields for distributing the fuel cell's gaseous reactants (i.e., hydrogen and oxygen) or coolant over the surfaces of the respective cathode and anode. These reactant flow fields generally include a plurality of lands that define a plurality of flow channels therebetween through which the gaseous reactants flow from a supply header at one end of the flow channels to an exhaust header at the opposite end of the flow channels. The fluid flowing to the flow field passes through an opening on the plate such that the fluid flows along a portion of both faces of the plate. The flowing of the fluid through the opening, however, results in a pressure drop which represents lost energy which is undesirable.
Typically, nonconductive gaskets or seals provide a seal and electrical insulation between the several plates of the fuel stack. In addition, the seals provide a flow path for the gaseous reactants from the supply header to the faces of the respective anode and cathode flow fields. Conventionally, the seals comprise a molded compliant material such as rubber. The molded rubber seals, however, are not suited to high-volume manufacture due to requiring several minutes of cure time and the difficulty of quickly and accurately placing the floppy seals on the plates. Additionally, the molded rubber seals are not conducive to use with a single piece conductive plate due to the lack of a seal support feature on portions of the single piece plate between the flow field and the headers.